A large variety of commercial airframes utilize a constant speed drive (CSD) and generator or an integrated drive generator (IDG) for generating three phase 400 Hz electrical power. The CSD and the CSD portion of the IDG function to convert a variable speed power takeoff from an aircraft propulsion engine gearbox into a constant shaft speed for driving a three phase alternator to produce three phase 400 Hz electrical power. Certain Boeing 747's, the McDonnell-Douglas DC-10 and many other aircraft utilize a CSD in which an outer drive shaft having first and second parts selectively couples a power takeoff from the aircraft engine outer gearbox when a clutch contained in the outer drive shaft is engaged. The clutch divides the outer drive shaft in to first and second parts. The outer concentric shaft is coupled by the internal CSD mechanism to the inner shaft which transmits torque from the output part of the inner drive shaft to drive the three phase alternator.
FIG. 1 illustrates a diagram of a prior art CSD disconnection mechanism which controls the engagement of a clutch coupling first and second parts of a drive shaft together. With respect to FIG. 1, a power takeoff from the aircraft engine is applied to a two part shaft 11 having a first part 12 which is coupled through a clutch 18 to a second part 14. The first part 12 and second part 14 is connected to the output 16 when the dog teeth of clutch 18 are engaged. Power from output 16 is applied to the carrier shaft of the CSD gear differential assembly (not illustrated). Inner shaft 17 applies power to a three phase alternator (not illustrated) mounted on an opposite side of a gearbox (not illustrated). A first segment 20 of clutch 18 is axially fixed in position The inner shaft 17 is driven at a constant velocity by the CSD gear differential assembly (not illustrated). A second segment 22 of the clutch 18 is axially movable between a first position, as illustrated, to a second position, as discussed below with reference to FIG. 2. A solenoid controlled plunger 24 causes an engagement of components which results in disengagement of the clutch 18 when released as illustrated in FIG. 2. Solenoid 26, as illustrated, holds the plunger 24 in a second extended position as illustrated in FIG. 1 by locking the moveable member in the second position against the force exerted by compressed spring 30. Upon application of a electric control signal through a control line (not illustrated) to solenoid 26, the member 28 of the solenoid withdraws into the solenoid to free plunger 24 to move from the second position to the first position as discussed below with reference to FIG. 2 under the force exerted by spring 30. A collar 32 having an outer threaded peripheral surface 33 rotates with the second part 14 of the shaft 12. End 34 of plunger 24 has threads which engage the threads of the peripheral surface 33 of collar 32.
FIG. 2 illustrates the disconnection mechanism of FIG. 1 after the plunger 24 has engaged the threaded collar 32 to cause the part 14 of the shaft and the part 22 of the clutch 18 to move axially to the left to disengage the clutch to decouple the second part 14 of the shaft 11 and output 16 from the first part 12. Like reference numerals identify like parts in FIGS. 1 and 2. After the clutch 18 is disengaged, the second part 14 of the shaft 11 and the output shaft 16 is reconnected to the first part 12 of the input shaft through the clutch 18 by pulling the plunger 24 downward to withdraw the threads of the end 34 of the plunger from contact with the threaded peripheral part of collar 32. Upon movement of the plunger 24 from the second position, as illustrated in FIG. 2 back to the first position, as illustrated in FIG. 1 spring 36 forces part 14 of the gearshaft assembly to the right to cause the first part 20 of the clutch 18 to engage the second part of the clutch 22 as illustrated in FIG. 1 to complete re-connection.
The aforementioned CSD in use in some models of Boeing 747's and on the McDonnell-Douglas DC-10 aircraft utilizes a disconnect mechanism similar to that described above with reference to FIGS. 1 and 2. This mechanism has the disadvantage that when CSD or IDG packaging and input shafting precludes the described designs when the previously described inner shaft 17 driving the alternator becomes the input shaft. In such cases it becomes necessary for the inner shaft of the two concentric shafts to include the disconnect. This has the disadvantage that it increases the overall axial length of the IDG with the concomitant weight penalty. Furthermore, overhung moment applied to the mounting flange of the casing of the CSD or IDG is significant enough to require increased cross-section for reinforcing of the flange which also results in a weight penalty. The overhung moment is a result of the mass of the CSD or IDG being supported by a mounting flange and the center of gravity of the mass being displaced away from the mounting flange.
U.S. Pat. No. 4,042,088, which is assigned to the assignee of the present invention, discloses a disconnect mechanism for use in a constant speed drive transmission.
U.S. Pat. No. 4,684,000, which is assigned to the assignee of the present invention, discloses a power transmission disconnect device with an operational interlock. Decoupling of an output shaft from an input shaft is accomplished by axial displacement of a clutch member. Displacement of the clutch from an engaged to a disengaged position is controlled by activation of an electric motor which drives a worm gear coupled to a throw out yoke for controlling the movement of the clutch from engaged to disengaged positions.
U.S. Pat. Nos. 2,642,970, 3,265,174, 3,713,518, 4,269,293, 4,393,965, and 4,562,908 disclose various forms of coupling mechanisms for controlling the application of rotary power.